JPWO2020217428A1 - Control device - Google Patents

Abstract

The control device (10) for controlling the self-excited power converter (20) connected to the AC system (101) is a phase generator (221) that generates the phase of the voltage command of the power converter (20). A voltage control unit (230) that generates a voltage value of a voltage command, and a command unit (250) that outputs a voltage command having a generated phase and a voltage value to a power converter are provided. The voltage control unit (230) calculates the compensation voltage value based on the voltage deviation between the reference voltage and the interconnection point voltage at the interconnection point between the AC system (101) and the power converter (20). When the unit (231) and the AC system (101) are independent systems that are not connected to the generator (51), the first droop value is calculated according to the magnitude of the interconnection point current flowing through the interconnection point. It includes a droop calculation unit (234) and a calculation unit (232) that calculates the voltage value of the voltage command based on the deviation between the compensation voltage value and the first droop value.

Description

The present disclosure relates to a control device for a power converter.

For high-voltage DC transmission, a power converter for converting AC power into DC power or converting DC power into AC power is adopted. Conventionally, a separately excited converter to which a thyristor is applied has been used as the power converter, but recently, a self-excited voltage converter has been used. There are various types of self-excited converters such as transformer multiplex system and modular multi-level system, but unlike separately excited converters, they can generate AC voltage by themselves, so power is supplied to the AC system to which a generator is not connected. it can.

For example, Japanese Patent Application Laid-Open No. 2018-129963 (Patent Document 1) discloses a control device for a power converter. This control device has a first switching unit that sets the AC current command value to 0 in response to the input of the black start command that operates without the power supply of the AC system, and the AC in response to the input of the black start command. The second switching unit that sets the current measurement value to the harmonic component other than the fundamental wave extracted from the AC current measurement value, and the AC voltage measurement value are set in advance according to the input of the black start command. It includes a third switching unit for setting the AC voltage command value.

JP-A-2018-129963

The operation method of the power converter connected to the AC system to which the power source (for example, the generator) is connected is different from the operation method of the power converter connected to the AC system to which the generator is not connected. .. Even if load fluctuations occur in an AC system to which a generator is not connected, the power converter is required to continue stable operation.

An object of the present disclosure is to provide a control device capable of continuing the operation of the power converter more stably when the power converter is connected to the AC system to which the generator is not connected. To provide.

According to certain embodiments, a control device for controlling a self-excited power converter connected to an AC system is provided. The control device outputs a phase generator that generates the phase of the voltage command of the power converter, a voltage control unit that generates the voltage value of the voltage command, and a voltage command having the generated phase and the voltage value to the power converter. It is equipped with a command unit to operate. The voltage control unit is a voltage compensation unit that calculates the compensation voltage value based on the voltage deviation between the reference voltage and the interconnection point voltage at the interconnection point between the AC system and the power converter, and the AC system is the generator. In the case of a single system that is not connected, it is based on the deviation between the compensation voltage value and the first droop value and the droop calculation unit that calculates the first droop value according to the magnitude of the interconnection point current flowing through the interconnection point. It also includes a calculation unit that calculates the voltage value of the voltage command.

According to the present disclosure, when the AC system to which the generator is not connected and the power converter are connected, the operation of the power converter can be continued more stably.

It is a figure which shows an example of the structure of a power control system. It is a schematic block diagram of a power converter. It is a circuit diagram which shows an example of the submodule which constitutes each leg circuit of FIG. It is a figure which shows an example of the hardware composition of a control device. It is a figure which shows an example of the functional structure of a control device. It is a figure for demonstrating the structure of the single system determination part. It is a figure which shows an example of the structure of the compensator of a voltage control part, and the droop arithmetic unit. It is a figure for demonstrating an example of the relationship between the interconnection point current and a voltage value. It is a figure for demonstrating another example of the functional structure of a control device. It is a figure for demonstrating another example of the relationship between the interconnection point current and a voltage value. It is a figure which shows the frequency droop characteristic. It is a figure which shows the non-linear frequency droop characteristic. It is a figure which shows an example of the structure of the frequency control part for shock mitigation. It is a figure which shows an example of the time change of a compensation angular frequency. It is a figure which shows another example of the structure of the frequency control part for shock mitigation. It is a figure which shows another example of the time change of a compensation angular frequency. It is a figure which shows an example of the functional structure of the control device for determining the transition of an AC system to an interconnection system. This is a timing chart for explaining the operation of the control device when the AC system shifts to the interconnection system. It is a figure which shows another example of the functional structure of the control device for determining the transition of an AC system to an interconnection system. It is a model diagram for demonstrating the determination method of the interconnection system determination part. It is a figure which shows the relationship between a phase difference and active power. It is a timing chart for demonstrating the determination method of the interconnection system determination unit. It is a figure which shows an example of the structure of the interconnection system determination part. It is a figure which shows another example of the configuration of a power control system. It is a figure which shows the modification of the structure of the voltage control part.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, the same parts are designated by the same reference numerals. Their names and functions are the same. Therefore, the detailed description of them will not be repeated.

<System configuration>
FIG. 1 is a diagram showing an example of a configuration of a power control system. As shown in FIG. 1, for example, a power control system is a system for controlling the power of a DC power transmission system. Electric power is transmitted and received between the two AC systems 101 and 102 via the DC transmission line 14P on the positive electrode side and the DC transmission line 14N on the negative electrode side, which are DC systems. Typically, the AC system 101 and the AC system 102 are three-phase AC systems.

A power converter 20 is connected to the AC system 101 via a transformer 13. Further, the generator 51 is connected to the AC system 101 via the circuit breaker 36. The AC system 101 includes buses 32, 33, a load 41, a load 42, and circuit breakers 34, 35, 36. L2 shows the system impedance between the bus 32 and the bus 33, and L3 shows the system impedance between the bus 33 and the generator 51.

The bus 32 is an interconnection point between the AC system 101 and the power converter 20. A load 41 is connected to the bus 32. A load 42 is connected to the bus 33. The circuit breaker 35 is provided between the bus 32 and the bus 33, and the circuit breaker 36 is provided between the bus 33 and the generator 51. When the circuit breaker 36 is in the closed state, the generator 51 is connected to the AC system 101, and when the circuit breaker 36 is in the open state, the generator 51 is not connected to the AC system 101.

The power converter 20 is connected between the AC system 101 and the DC transmission lines 14P and 14N (hereinafter, also collectively referred to as “DC transmission line 14”). A generator 63 is connected to the AC system 102, and a power converter 21 is connected via a transformer 61. The power converter 21 performs power conversion between the AC system 102 and the DC transmission line 14.

For example, electric power is transmitted from the AC system 102 to the AC system 101. In this case, the power converter 20 operates as a forward converter (REC: Rectifier), and the power converter 21 operates as an inverse converter (INV: Inverter). Specifically, the power converter 21 converts the AC power into DC power, and the converted DC power is transmitted to DC via the DC transmission line 14. At the power receiving end, DC power is converted into AC power by the power converter 20 and supplied to the AC system 101 via the transformer 13. When the power converter 21 operates as an inverse converter and the power converter 20 operates as a forward converter, the conversion operation opposite to the above is performed.

The power converter 20 is composed of a self-excited voltage type power converter. For example, the power converter 20 is composed of a modular multi-level converter including a plurality of submodules connected in series with each other. The "submodule" is also called the "transducer cell". The power converter 21 is also composed of a self-excited voltage type power converter.

The control device 10 acquires the amount of electricity used for control (for example, current, voltage, etc.) from a plurality of detectors. The control device 10 controls the operation of the power converter 20 based on the amount of electricity acquired from the plurality of detectors. The control device 10 is configured to be able to communicate with the control device 12. The control device 12 controls the operation of the power converter 21 based on the amount of electricity acquired from the plurality of detectors. The control device 12 has the same configuration as the control device 10.

In the present embodiment, since the power converter 20 is a self-excited power converter, the power converter 20 is operated as a power source (that is, a voltage source) of the AC system 101 to supply power from the power converter 20. By doing so, the AC system 101 can be restored from the power failure state.

Specifically, the power converter 20 has a black start function for recovering the AC system 101 from a power failure state even when the circuit breaker 36 is opened and the generator 51 is not connected to the AC system 101. ing. It is assumed that various emergency power supplies (for example, control device power supply, auxiliary power supply, etc.) that enable the operation of the power converter 20 even when the AC system 101 is in a power failure state are secured. .. Alternatively, in the event of a power failure in the AC system 101, the power converter 20 may be operated by receiving power from the generator 63 via the DC transmission line 14.

For example, the control device 10 controls the power converter 20 to start up the AC system 101 in the following procedure. In the initial state, the circuit breakers 34 to 36 are assumed to be in the open state. First, the power converter 20 is started up by receiving power from the DC transmission line 14 side.

Subsequently, the circuit breaker 34 is closed, and the power converter 20 is connected to the bus 32, which is the interconnection point with the AC system 101. At this time, the power converter 20 is connected to the AC system 101 to which the generator 51 is not connected. In the specification of the present application, the AC system 101 in a state of not being connected to the generator 51 is also referred to as a “single system”. In this case, the control device 10 operates the power converter 20 by a constant voltage constant frequency (CVCF) control method to make the power converter 20 function as a voltage source of the AC system 101.

After that, the circuit breaker 35 and the circuit breaker 36 are closed in order. When the circuit breaker 36 is closed, the generator 51 is connected to the AC system 101. At this time, the power converter 20 is connected to the AC system 101 to which the generator 51 is connected. In the specification of the present application, the AC system 101 in a state of being connected to the generator 51 is also referred to as an “interconnection system”.

The generator 51 has a frequency droop control function, and when the frequency increases according to a predetermined inclination (that is, the adjustment rate), the generator output (that is, the active power output of the generator) is reduced, and the frequency is increased. When is decreased, the active power output is increased. Therefore, when the AC system 101 to which the generator 51 is connected and the power converter 20 are connected, the control device 10 shifts the power converter 20 to another control method (for example, a frequency droop control method) different from the CVCF control method. Switch the control method of. The frequency of the AC system 101 is kept constant by the cooperation between the power converter 20 and the generator 51 connected to the AC system 101.

<Power converter configuration>
(overall structure)
FIG. 2 is a schematic configuration diagram of the power converter 20. With reference to FIG. 2, the power converter 20 is connected in parallel between the positive electrode DC terminal (that is, the high potential side DC terminal) Np and the negative electrode DC terminal (that is, the low potential side DC terminal) Nn. Including a plurality of leg circuits 4u, 4v, 4w (hereinafter, also collectively referred to as “leg circuit 4”). The leg circuit 4 is provided in each of the plurality of phases constituting the alternating current. The leg circuit 4 performs power conversion between the AC system 101 and the DC transmission line 14. In FIG. 2, three leg circuits 4u, 4v, and 4w are provided corresponding to the U phase, V phase, and W phase of the AC system 101, respectively.

The AC input terminals Nu, Nv, Nw provided in the leg circuits 4u, 4v, 4w, respectively, are connected to the transformer 13. In FIG. 1, the connection between the AC input terminals Nv, Nw and the transformer 13 is not shown for ease of illustration. The high-potential side DC terminal Np and the low-potential side DC terminal Nn commonly connected to each leg circuit 4 are connected to the DC transmission line 14.

Instead of using the transformer 13 of FIG. 1, a configuration using an interconnection reactor may be used. Further, instead of the AC input terminals Nu, Nv, Nw, the leg circuits 4u, 4v, 4w are provided with primary windings, respectively, and the leg circuits 4u, 4v, 4w are provided via the secondary windings magnetically coupled to the primary windings. May be connected to the transformer 13 or the interconnection reactor in an alternating current manner. In this case, the primary winding may be the following reactors 8A and 8B. That is, the leg circuit 4 is electrically (that is, DC or AC) through the connection portion provided in each leg circuit 4u, 4v, 4w such as the AC input terminals Nu, Nv, Nw or the above-mentioned primary winding. It is connected to the AC system 101.

The leg circuit 4u includes an upper arm 5 from the high potential side DC terminal Np to the AC input terminal Nu, and a lower arm 6 from the low potential side DC terminal Nn to the AC input terminal Nu. The AC input terminal Nu, which is the connection point between the upper arm 5 and the lower arm 6, is connected to the transformer 13. The high potential side DC terminal Np and the low potential side DC terminal Nn are connected to the DC transmission line 14. Since the leg circuits 4v and 4w have the same configuration, the leg circuits 4u will be described below as a representative.

The upper arm 5 includes a plurality of cascaded submodules 7 and a reactor 8A. The plurality of submodules 7 and the reactor 8A are connected in series with each other. Similarly, the lower arm 6 includes a plurality of cascaded submodules 7 and a reactor 8B. The plurality of submodules 7 and the reactor 8B are connected in series with each other.

The position where the reactor 8A is inserted may be any position of the upper arm 5 of the leg circuit 4u, and the position where the reactor 8B is inserted may be any position of the lower arm 6 of the leg circuit 4u. Good. There may be a plurality of reactors 8A and 8B, respectively. The inductance values of each reactor may be different from each other. Further, only the reactor 8A of the upper arm 5 or only the reactor 8B of the lower arm 6 may be provided.

The reactors 8A and 8B are provided so that the accident current does not suddenly increase in the event of an accident such as an AC system 101 or a DC transmission line 14. However, if the inductance values of the reactors 8A and 8B are made excessive, there arises a problem that the efficiency of the power converter is lowered. Therefore, in the event of an accident, it is preferable to stop (turn off) all the switching elements of each submodule 7 in the shortest possible time.

The power converter 20 further includes an AC voltage detector 81, an AC current detector 82, and a DC voltage detector 11A as each detector for measuring the amount of electricity (for example, current, voltage, etc.) used for control. , 11B and arm current detectors 9A and 9B provided in each leg circuit 4.

The signals detected by these detectors are input to the control device 10. The control device 10 outputs control commands 15pu, 15nu, 15pv, 15nv, 15pw, 15nw for controlling the operating state of each submodule 7 based on these detection signals. Further, the control device 10 receives the signal 17 from each submodule 7. The signal 17 includes a detected value of the voltage of the DC capacitor 24 in FIG. 3 described later.

The control commands 15pu, 15nu, 15pv, 15nv, 15pw, and 15nw (hereinafter, also collectively referred to as "control command 15") are U-phase upper arm, U-phase lower arm, V-phase upper arm, V-phase lower arm, and W-phase. It is generated corresponding to the upper arm and the W phase lower arm, respectively.

In FIG. 1, in order to facilitate the illustration, the signal line of the signal input from each detector to the control device 10 and the signal line of the signal input / output between the control device 10 and each submodule 7 are shown. Although some of them are described together, they are actually provided for each detector and each submodule 7. The signal lines between each submodule 7 and the control device 10 may be provided separately for transmission and reception. Further, in the case of the present embodiment, these signals are transmitted via an optical fiber from the viewpoint of noise resistance.

Hereinafter, each detector will be specifically described. The AC voltage detector 81 detects the U-phase AC voltage value Vacu, the V-phase AC voltage value Vacv, and the W-phase AC voltage value Vacw of the bus 32, which is the interconnection point. In the following description, the three-phase AC voltage values Vaccu, Vaccv, and Vacw are also collectively referred to as interconnection point voltage Vs.

The AC current detector 82 detects the U-phase AC current value Iacu, the V-phase AC current value Iacv, and the W-phase AC current value Iacw flowing through the interconnection point. In the following description, the three-phase AC current values Iacu, Iacv, and Iacw are collectively referred to as the interconnection point current Is. The DC voltage detector 11A detects the DC voltage value Vdcp of the high potential side DC terminal Np connected to the DC transmission line 14. The DC voltage detector 11B detects the DC voltage value Vdcn of the low potential side DC terminal Nn connected to the DC transmission line 14.

The arm current detectors 9A and 9B provided in the U-phase leg circuit 4u detect the upper arm current Ipu flowing through the upper arm 5 and the lower arm current Inu flowing through the lower arm 6, respectively. Similarly, the arm current detectors 9A and 9B provided in the V-phase leg circuit 4v detect the upper arm current Ipv and the lower arm current Inv, respectively. The arm current detectors 9A and 9B provided in the leg circuit 4w for the W phase detect the upper arm current Ipw and the lower arm current Inw, respectively.

(Submodule configuration example)
FIG. 3 is a circuit diagram showing an example of submodules constituting each leg circuit of FIG. The sub-module 7 shown in FIG. 3 includes a half-bridge type conversion circuit 25, a DC capacitor 24 as an energy storage device, a DC voltage detection unit 27, a transmission / reception unit 28, and a gate control unit 29.

The half-bridge type conversion circuit 25 includes switching elements 22A and 22B connected in series with each other and diodes 23A and 23B. The diodes 23A and 23B are connected to the switching elements 22A and 22B in antiparallel (that is, in parallel and in the antibias direction), respectively. The DC capacitor 24 is connected in parallel with the series connection circuit of the switching elements 22A and 22B to hold the DC voltage. The connection nodes of the switching elements 22A and 22B are connected to the input / output terminals 26P on the high potential side. The connection node between the switching element 22B and the DC capacitor 24 is connected to the input / output terminal 26N on the low potential side.

The gate control unit 29 operates in accordance with the control command 15 received from the control device 10. During normal operation (that is, when a zero voltage or a positive voltage is output between the input / output terminals 26P and 26N), the gate control unit 29 turns one of the switching elements 22A and 22B on and the other off. Control so that When the switching element 22A is in the ON state and the switching element 22B is in the OFF state, a voltage between both ends of the DC capacitor 24 is applied between the input / output terminals 26P and 26N. On the contrary, when the switching element 22A is in the off state and the switching element 22B is in the on state, the voltage between the input / output terminals 26P and 26N is 0V.

Therefore, the sub-module 7 shown in FIG. 3 can output a zero voltage or a positive voltage depending on the voltage of the DC capacitor 24 by alternately turning on the switching elements 22A and 22B.

On the other hand, when the control device 10 detects an overcurrent of the arm current, the control device 10 transmits a gate block (that is, turning off of the switching element) command to the transmission / reception unit 28. When the gate control unit 29 receives the gate block command via the transmission / reception unit 28, the gate control unit 29 turns off both the switching elements 22A and 22B for circuit protection. As a result, for example, in the case of a ground fault in the AC system 101, the switching elements 22A and 22B can be protected.

The DC voltage detection unit 27 detects the voltage between 24P and 24N across the DC capacitor 24. The transmission / reception unit 28 transmits the control command 15 received from the control device 10 to the gate control unit 29, and transmits a signal 17 representing the voltage of the DC capacitor 24 detected by the DC voltage detection unit 27 to the control device 10.

The DC voltage detection unit 27, the transmission / reception unit 28, and the gate control unit 29 may be configured by a dedicated circuit, or may be configured by using an FPGA (Field Programmable Gate Array) or the like. For each of the switching elements 22A and 22B, a self-extinguishing type switching element capable of controlling both on operation and off operation is used. The switching elements 22A and 22B are, for example, an IGBT (Insulated Gate Bipolar Transistor) or a GCT (Gate Commutated Turn-off thyristor).

The configuration of the submodule 7 described above is an example, and submodules 7 having other configurations may be applied to the present embodiment. For example, the sub-module 7 may be configured by using a full-bridge type conversion circuit or a sleek quarter-bridge type conversion circuit. The sleek quarter bridge type conversion circuit is also called a semi-full bridge type conversion circuit, and has a configuration in which one on / off switching semiconductor is omitted in the full bridge type conversion circuit.

<Hardware configuration of control device>
FIG. 4 is a diagram showing an example of the hardware configuration of the control device 10. With reference to FIG. 4, the output control device 10 includes an auxiliary transformer 55, a signal conversion unit 56, and an arithmetic processing unit 70. For example, the control device 10 is configured as a digital protection control device.

The auxiliary transformer 55 takes in the amount of electricity from each detector, converts it into a voltage signal suitable for signal processing in the internal circuit, and outputs it. The signal conversion unit 56 takes in an analog signal (that is, a voltage signal) output from the auxiliary transformer 55 and converts it into a digital signal. Specifically, the signal conversion unit 56 includes an analog filter, a sample hold circuit, a multiplexer, and an AD converter.

The analog filter removes high frequency noise components from the voltage signal output from the auxiliary transformer 55. The sample hold circuit samples the signal output from the analog filter at a predetermined sampling cycle. Based on the timing signal input from the arithmetic processing unit 70, the multiplexer sequentially switches the waveform signals input from the sample hold circuit in chronological order and inputs them to the AD converter. The AD converter converts the waveform signal input from the multiplexer from analog data to digital data. The AD converter outputs the digitally converted waveform signal (digital data) to the arithmetic processing unit 70.

The arithmetic processing unit 70 communicates with a CPU (Central Processing Unit) 72, a ROM 73, a RAM 74, a DI (digital input) circuit 75, a DO (digital output) circuit 76, and an input interface (I / F) 77. Includes interface (I / F) 78. These are connected by a bus 71.

The CPU 72 controls the operation of the control device 10 by reading and executing a program stored in the ROM 73 in advance. The ROM 73 stores various information used by the CPU 72. The CPU 72 is, for example, a microprocessor. The hardware may be an FPGA other than a CPU, an ASIC (Application Specific Integrated Circuit), or a circuit having other arithmetic functions.

The CPU 72 takes in digital data from the signal conversion unit 56 via the bus 71. The CPU 72 executes a control operation using the captured digital data according to a program stored in the ROM 73.

The CPU 72 outputs a control command to the outside via the DO circuit 76 based on the control calculation result. Further, the CPU 72 receives a response to the control command via the DI circuit 75. The input interface 77 is typically various buttons and the like, and receives various setting operations from the system operator. Further, the CPU 72 transmits and receives various information to and from other devices via the communication interface 78.

<Judgment method for transition to a single system>
A determination method for determining whether or not the AC system 101 connected to the power converter 20 has shifted from the interconnection system to the single system will be described with reference to FIGS. 5 and 6.

FIG. 5 is a diagram showing an example of the functional configuration of the control device 10. With reference to FIG. 5, the control device 10 includes a voltage calculation unit 201, a current calculation unit 209, a single system determination unit 211, a frequency control unit 220, a voltage control unit 230, and a command unit 250. Each of these functions is realized, for example, by the CPU 72 of the arithmetic processing unit 70 executing a program stored in the ROM 73. Note that some or all of these functions may be configured to be realized by hardware.

The voltage calculation unit 201 acquires the three-phase interconnection point voltage Vs detected by the AC voltage detector 81, and calculates the absolute voltage value | Vs | indicating the magnitude of the interconnection point voltage Vs and the phase error Δθ. To do. Specifically, the voltage calculation unit 201 includes a dq conversion unit 202, a voltage calculation unit 203, and a phase error calculation unit 204.

The dq conversion unit 202 dq-converts the interconnection point voltage Vs using the phase θ of the voltage command of the power converter 20, and calculates Vd0, which is a d-axis component of the interconnection point voltage, and Vq0, which is a q-axis component. .. The dq conversion unit 202 removes the harmonic components of the d-axis component Vd0 and the q-axis component Vq0 by low-pass filter processing, and calculates the d-axis component Vd and the q-axis component Vq from which the harmonic components have been removed. The phase θ is generated by the frequency control unit 220, which will be described later.

The voltage calculation unit 203 converts the d-axis component Vd and the q-axis component Vq into polar coordinates to calculate the amplitude component. Specifically, the voltage calculation unit 203 calculates the absolute voltage value | Vs | indicating the magnitude of the interconnection point voltage Vs. Typically, the absolute voltage value | Vs | is the amplitude value or the effective value of the interconnection point voltage Vs.

The phase error calculation unit 204 polar-coordinates the d-axis component Vd and the q-axis component Vq to calculate the phase component. This phase component corresponds to the phase error Δθ, which is the phase difference between the phase θ of the voltage command of the power converter 20 and the phase of the interconnection point voltage Vs. This is because the dq conversion unit 202 dq-converts the interconnection point voltage Vs by the phase θ of the voltage command of the power converter 20.

The current calculation unit 209 acquires the three-phase interconnection point current Is detected by the AC current detector 82, and calculates the absolute current value | Is | indicating the magnitude of the interconnection point current Is. Typically, the absolute current value | Vs | is the amplitude value or effective value of the interconnection point current Is.

The frequency control unit 220 includes a phase generation unit 221. The phase generation unit 221 generates the phase θ of the voltage command of the power converter 20, and outputs the phase θ to the command unit 250 and the voltage calculation unit 201. The phase generator 221 includes a compensator 222, an adder 223, a time integrator 224, and a switch 225.

The compensator 222 receives the input of the phase error Δθ, calculates the compensation angular frequency Δω for compensating for the phase error Δθ, and outputs the compensation angular frequency Δω. Specifically, the compensation angular frequency Δω is an angular frequency for making the phase error Δθ zero. The compensator 222 is composed of a feedback controller such as a PI controller (Proportional-Integral Controller), for example.

The switch 225 is controlled to the ON state when the AC system 101 is an interconnection system, and is controlled to an OFF state when the AC system 101 is a single system.

When the AC system 101 is an interconnection system and the switch 225 is controlled in the ON state, the frequency control unit 220 generates the phase θ by the control method in the interconnection system mode. Specifically, the adder 223 of the phase generator 221 adds the reference angular frequency ω0 of the power converter 20 and the compensation angular frequency Δω, and outputs the sum of the angular frequencies ω to the time integrator 224. .. The time integrator 224 calculates the phase θ of the voltage command of the power converter 20 by time-integrating the angular frequency ω, and outputs the phase θ to the command unit 250. Since the phase θ is an angle, a multiple of 360 ° may be added or subtracted so as to be within the range of ± 180 °. The details of the operation of the frequency control unit 220 when the switch 225 is controlled to the OFF state will be described later.

The switch 260 is controlled to the OFF state when the AC system 101 is an interconnection system, and is controlled to an ON state when the AC system 101 is a single system.

The adder / subtractor 262 calculates the voltage deviation ΔVr between the reference voltage value Vref and the absolute voltage value | Vs |. The deviation ΔV output from the adder / subtractor 262 is input to the voltage control unit 230.

The voltage control unit 230 generates the voltage value V of the voltage command. Specifically, the voltage control unit 230 includes a compensator 231, an addition / subtractor 232, and a droop arithmetic unit 234 (corresponding to “Fdi” in FIG. 5).

When the AC system 101 is an interconnection system and the switch 260 is controlled in the OFF state, the voltage control unit 230 generates the voltage value V by the control method in the interconnection system mode. Specifically, the compensator 231 calculates the compensating voltage value based on the voltage deviation ΔVr. Specifically, the compensation voltage value is a voltage value for making the voltage deviation ΔVr zero. Since the absolute current value | Is | is not input to the droop calculator 234, the droop calculator 234 does not output the droop value corresponding to the absolute current value | Is |. Therefore, the adder / subtractor 232 outputs the compensation voltage value as the voltage value V of the voltage command to the command unit 250. The details of the operation of the voltage control unit 230 when the switch 260 is controlled to the ON state will be described later.

The command unit 250 generates a voltage command having a phase θ generated by the frequency control unit 220 and a voltage value V generated by the voltage control unit 230, and outputs the voltage command to the power converter 20 as a control command. .. When the AC system 101 is an interconnection system, the power converter 20 can generate a voltage synchronized with the interconnection system.

Here, it is assumed that the generator 51 is disconnected from the AC system 101 due to an accident or the like, and the AC system 101 shifts from the interconnection system to the independent system. In the present embodiment, the single system determination unit 211 detects the transition from the interconnection system to the single system. Specifically, the single system determination unit 211 determines whether or not the AC system 101 has shifted from the interconnection system to the single system based on the phase error Δθ and the absolute voltage value | Vs | of the interconnection point voltage Vs. To judge.

FIG. 6 is a diagram for explaining the configuration of the single system determination unit 211. With reference to FIG. 6, the independent system determination unit 211 includes a voltage determination circuit 301, a phase determination circuits 302 and 303, a rate of change determination circuit 304, an OR circuit 305, and an AND circuit 306.

The voltage determination circuit 301 determines whether or not the absolute voltage value | Vs | is less than the voltage threshold value Vth. Specifically, the voltage determination circuit 301 outputs an output value "1" to the AND circuit 306 when it is determined that | Vs | <Vth is satisfied, and when it is determined that it is not, the output value is not. “0” is output to the AND circuit 306.

The phase determination circuit 302 determines whether or not the phase error Δθ is larger than the threshold value θ1. Specifically, the phase determination circuit 302 outputs an output value "1" to the OR circuit 305 when it is determined that Δθ> θ1 is satisfied, and an output value “0” when it is determined otherwise. Is output to the OR circuit 305.

The phase determination circuit 303 determines whether or not the phase error Δθ is less than the threshold value θ2 (however, θ2 <θ1). Specifically, the phase determination circuit 303 outputs an output value "1" to the OR circuit 305 when it is determined that Δθ <θ2 is satisfied, and an output value “0” when it is determined otherwise. Is output to the OR circuit 305.

The change rate determination circuit 304 determines whether or not the change rate dΔθ / dt of the phase error Δθ is larger than the reference change rate Ra. Specifically, the change rate determination circuit 304 outputs an output value "1" to the AND circuit 306 when it is determined that dΔθ / dt> Ra is satisfied, and outputs an output value "1" when it is determined otherwise. The value "0" is output to the AND circuit 306.

The OR circuit 305 performs an OR operation on each output value of the phase determination circuits 302 and 303. Specifically, if at least one of these output values is "1", the OR circuit 305 outputs the output value "1" to the AND circuit 306, otherwise the output value ". 0 ”is output to the AND circuit 306.

The AND circuit 306 performs an AND operation on a value obtained by inverting the logic level of the output of the voltage determination circuit 301, an output value of the OR circuit 305, and a value obtained by inverting the logic level of the output of the rate of change determination circuit 304.

Specifically, in the AND circuit 306, the AC system 101 is an interconnection system in the AND circuit 306 when | Vs | <Vth is not satisfied, at least one of Δθ> θ1 and Δθ <θ2 is satisfied, and dΔθ / dt> Ra is not satisfied. Outputs a signal (that is, an output value "1") indicating that the system has shifted to a single system.

The reason why the single system determination unit 211 determines the transition from the interconnection system to the single system by the above logic will be described. Specifically, if the generator 51 is disconnected from the AC system 101 for some reason, the power converter 20 cannot execute frequency control in cooperation with the generator 51. Therefore, the frequency starts to shift due to the imbalance of power supply and demand, and the phase error Δθ becomes large and falls outside the reference range (that is, Δθ> θ1 or Δθ <θ2).

Here, the reason why the voltage determination circuit 301 and the rate of change determination circuit 304 are provided is to prevent the occurrence of a transient accident in the AC system 101 from being erroneously determined as the transition of the AC system 101 to a single system. Is.

Specifically, when a transient accident occurs in the AC system 101, the voltage value at the interconnection point drops and the phase also changes. Therefore, when the absolute voltage value | Vs | is less than the voltage threshold value Vth, it is highly probable that an accident has occurred in the AC system 101. Therefore, even when the phase error Δθ is out of the reference range, if the absolute voltage value | Vs | is less than the voltage threshold Vth, the AND circuit 306 has shifted the AC system 101 to a single system. (That is, the output value “1”) is not output.

In addition, when a transient accident occurs, the phase error Δθ changes abruptly due to system disturbance. Therefore, when the rate of change dΔθ / dt of the phase error Δθ is larger than the reference rate of change Ra, it is highly probable that an accident has occurred in the AC system 101. Therefore, even when the phase error Δθ is out of the reference range, the AND circuit 306 does not output the output value “1” when the rate of change dΔθ / dt is larger than the reference rate of change Ra.

The single system determination unit 211 may be configured to prevent the above-mentioned erroneous determination by at least one of the voltage determination circuit 301 and the rate of change determination circuit 304.

Even if an off-delay timer is provided between the voltage determination circuit 301 and the AND circuit 306 in order to more accurately distinguish between a transient accident and the transition of the AC system 101 to a single system. Good. Specifically, immediately after a transient accident occurs, the voltage value at the interconnection point drops, so an output value "1" is output from the voltage determination circuit 301, and this output value "1" is output by the off-delay timer. Is maintained for time T1.

Further, since the phase of the interconnection point voltage also changes, the phase error Δθ is out of the reference range, but the AND circuit 306 outputs the output value “from the detection of the decrease in the interconnection point voltage value until the time T1 elapses. 1 ”is not output. After that, when the transient accident is resolved, the voltage value and phase of the interconnection point return to the normal state, and the phase error Δθ is within the reference range. Also in this case, the AND circuit 306 does not output the output value “1”. In this way, by maintaining the output value "1" for the time T1 by the off-delay timer, it is possible to more accurately prevent the occurrence of a transient accident from being erroneously determined as the transition of the AC system 101 to a single system. can do.

When the AC system 101 shifts to a single system, the output value "1" is output from the AND circuit 306 in order to maintain the phase error Δθ outside the reference range, unlike a transient accident. ..

Summarizing the above determination methods, the single system determination unit 211 determines the condition C1 that the phase error Δθ is out of the reference range (that is, Δθ> θ1 or Δθ <θ2), and the absolute voltage value of the interconnection point voltage Vs. When the condition C2 that | Vs | is larger than the voltage threshold Vth and the condition C3 that the rate of change of the phase error Δθ is less than the reference change rate Ra are satisfied, the AC system 101 is independent from the interconnection system. It is judged that the system has been transferred. In addition, the independent system determination unit 211 determines that the AC system 101 has shifted from the interconnection system to the independent system when the condition C1 and the condition C2 are satisfied, or when the condition C1 and the condition C3 are satisfied. You may.

<Control method for single system and interconnection>
Next, with reference to FIGS. 5, 7 and 8, a control method of the power converter 20 when the power converter 20 is connected to the AC system 101 which has been transferred to the independent system will be described.

With reference to FIG. 5, when the independent system determination unit 211 determines that the AC system 101 has shifted to the independent system, it outputs an OFF signal to the switch 225 and an ON signal to the switch 260. As a result, the switch 225 is turned off and the switch 260 is turned on.

When the AC system 101 is a single system, the frequency control unit 220 generates the phase θ by the control method in the single system mode. Specifically, the Δω output from the compensator 222 of the phase generation unit 221 is not input to the adder 223. Therefore, the phase generation unit 221 generates the phase θ of the voltage command by time-integrating the reference angular frequency ω0.

Specifically, the adder 223 outputs the reference angular frequency ω0 of the power converter 20 to the time integrator 224 as the angular frequency ω. The time integrator 224 calculates the phase θ of the voltage command by time-integrating the angular frequency ω (that is, the reference angular frequency ω0), and outputs the phase θ to the command unit 250. In this case, since the phase θ does not fluctuate, the power converter 20 that receives the voltage command having the phase θ from the command unit 250 generates a voltage having a constant frequency.

Further, when the AC system 101 is a single system, the switch 260 is turned on. In this case, the voltage control unit 230 generates the voltage value V by the control method in the single system mode. Specifically, the absolute current value | Is | calculated by the current calculation unit 209 is input to the droop calculation unit 234 of the voltage control unit 230. The droop calculator 234 calculates the droop value according to the absolute current value | Is | and outputs it to the adder / subtractor 232.

FIG. 7 is a diagram showing an example of the configuration of the compensator 231 and the droop arithmetic unit 234 of the voltage control unit 230. With reference to FIG. 7, the compensator 231 calculates the compensated voltage value by performing a first-order delay process on the value compensated for the voltage deviation ΔVr, and outputs the compensated voltage value to the adder / subtractor 232. Specifically, the compensator 231 includes a PI controller 231x and a first-order lag element 231y.

The PI controller 231x receives the input of the voltage deviation ΔVr and outputs the value feedback-controlled so as to compensate for the voltage deviation ΔVr to the first-order lag element 231y.

The first-order lag element 231y is a filter represented by the transfer function G1 (= 1 / (1 + Ts)). The first-order lag element 231y performs filter processing (that is, first-order lag processing) by the transfer function G1 on the value output from the PI controller 231x to calculate the compensation voltage value, and outputs the compensation voltage value to the addition / subtractor 232.

The droop calculator 234 calculates the droop value DIs by performing an inexact differential process on the absolute current value | Is | and multiplying it by Di. Specifically, the droop arithmetic unit 234 includes an inexact differential element 234x and a droop coefficient element 234y.

The inexact differential element 234x is a filter represented by the transfer function G2 (= Ts / (1 + Ts)). The inexact differential element 234x performs a filter process (that is, an inexact differential process) by the transfer function G2 on the current absolute value | Is | and outputs the current absolute value | Is | to the droop coefficient element 234y. A dead band element may be inserted in front of the incomplete differential element 234x (that is, between the switch 260 and the incomplete differential element 234x). As a result, unnecessary operation when the current is small can be suppressed.

The droop coefficient element 234y outputs the droop value DIs obtained by multiplying the absolute current value | Is | subjected to the inexact differential processing by Di to the adder / subtractor 232. The coefficient Di is a coefficient indicating the slope of the current droop characteristic of the droop calculator 234. The droop value DIs is a voltage value for correcting the compensation voltage value.

The adder / subtractor 232 calculates the deviation between the compensation voltage value and the droop value DIs as the voltage value V of the voltage command, and outputs the voltage value V to the command unit 250. The adder / subtractor 232 functions as a calculation unit for calculating the voltage value V.

FIG. 8 is a diagram for explaining an example of the relationship between the interconnection point current Is and the voltage value V. With reference to FIG. 8, when an accident occurs on the AC system 101 side, the interconnection point current Is suddenly changes due to a steep voltage fluctuation of the interconnection point voltage Vs. In this case, the larger the absolute current value | Is |, the larger the droop value DIs. This is because the absolute current value | Is | is subjected to an inexact differential process. The larger the absolute current value | Is |, the smaller the deviation between the compensation voltage value and the droop value DIs (that is, the voltage value V). Therefore, the voltage value V becomes as shown in Graph 601 according to the interconnection point current Is. Change. As described above, by reducing the voltage value V as the absolute current value | Is | increases, it is possible to prevent an overcurrent from flowing through the power converter 20 and continue the operation.

On the other hand, when the interconnection point current Is changes slowly due to a gradual voltage fluctuation of the interconnection point voltage Vs, the droop value DIs is extremely high because the absolute current value | Is | is subjected to inexact differential processing. Becomes smaller. In this case, the voltage value V becomes substantially the same as the compensation voltage value output from the compensator 231 and is kept constant as shown in Graph 603. Specifically, the voltage value V is fixed in the vicinity of the reference voltage value Vref. That is, even when the interconnection point current Is is inductive (that is, the delayed reactive current in the direction flowing out from the power converter 20 to the AC system 101 side is negative), the interconnection point current Is is capacitive (that is, power). Even when the delayed reactive current in the direction of outflow from the converter 20 is positive), the voltage value V is constant.

According to the above configuration, when an accident occurs on the AC system 101 side, which is a single system, and a steep voltage fluctuation occurs, the control device 10 reduces the voltage output from the power converter 20 to generate an overcurrent. Can be suppressed. Further, when a gradual voltage fluctuation on the AC system 101 side occurs, the control device 10 can output a constant voltage from the power converter 20.

(Modification example)
A modified example of the control method of the power converter 20 when the AC system 101 is a single system will be described with reference to FIGS. 9, 10 and 11.

FIG. 9 is a diagram for explaining another example of the functional configuration of the control device 10. With reference to FIG. 9, the control device 10A includes a voltage calculation unit 201, an active power calculation unit 205, an ineffective power calculation unit 207, a current calculation unit 209, an independent system determination unit 211, and a frequency control unit 220A. , A voltage control unit 230A, a command unit 250, a switch 260, and an adder / subtractor 262. Here, a functional configuration different from the functions shown in FIG. 5 will be described. The control device 10A corresponds to the control device 10 shown in FIG. 1, but is provided with an additional reference numeral such as “A” for convenience in order to distinguish it from the control device 10 shown in FIG.

The active power calculation unit 205 calculates the active power P at the interconnection point. Specifically, the active power calculation unit 205 is based on the interconnection point voltage Vs detected by the AC voltage detector 81 and the interconnection point current Is detected by the AC current detector 82. The active power P in is calculated.

The ineffective power calculation unit 207 calculates the ineffective power Q at the interconnection point. Specifically, the disabling power calculation unit 207 calculates the disabling power Q at the interconnection point based on the interconnection point voltage Vs and the interconnection point current Is.

The voltage control unit 230A corresponds to a configuration in which a droop calculator 235 (corresponding to “Fdq” in FIG. 9) and an adder / subtractor 236 are added to the voltage control unit 230 in FIG. The droop calculator 235 receives the input of the negative power Q calculated by the negative power calculation unit 207. The droop calculator 235 calculates the droop value Dqs according to the ineffective power Q and outputs it to the adder / subtractor 236. Specifically, the droop value Dqs is a value obtained by multiplying the ineffective power Q by Dq. The coefficient Dq is a coefficient indicating the slope of the voltage droop characteristic of the droop calculator 235. The voltage droop characteristic has a characteristic that the voltage decreases as the reactive power output (that is, the delayed reactive current in the direction flowing out from the power converter 20) increases. The configuration may be such that a reactive current is used instead of the reactive power.

The adder / subtractor 236 receives an input of the voltage deviation ΔVr from the adder / subtractor 262, and receives an input of the droop value Dqs from the droop calculator 235. The adder / subtractor 236 subtracts the droop value Dqs from the voltage deviation ΔVr, and outputs the subtracted value ΔVrq (hereinafter, also referred to as “subtracted value ΔVrq”) to the compensator 231. The compensator 231 calculates the compensating voltage value based on the subtraction value ΔVrq. Specifically, the compensator 231 calculates the compensation voltage value by performing a primary delay process on the value compensated for the subtraction value ΔVrq, and outputs the compensation voltage value to the adder / subtractor 232. More specifically, the PI controller 231x receives the input of the subtraction value ΔVrq and outputs the value feedback-controlled so as to compensate the subtraction value ΔVrq to the first-order lag element 231y. The first-order lag element 231y performs filtering processing by the transfer function G1 on the value output from the PI controller 231x to calculate the compensation voltage value, and outputs the compensation voltage value to the addition / subtractor 232.

The adder / subtractor 232 calculates the deviation between the compensation voltage value and the droop value DIs as the voltage value V of the voltage command, and outputs the voltage value V to the command unit 250.

FIG. 10 is a diagram for explaining another example of the relationship between the interconnection point current Is and the voltage value V. With reference to FIG. 10, when the interconnection point current Is changes abruptly, the voltage value V changes as shown in Graph 601 according to the interconnection point current Is, as in FIG. That is, the larger the absolute current value | Is |, the smaller the voltage value V. Therefore, even if an accident occurs on the AC system 101 side, which is a single system, the occurrence of overcurrent can be suppressed.

On the other hand, when the interconnection point current Is changes slowly, the voltage value V is not constant as shown in FIG. 8, but changes slowly according to the interconnection point current Is. This is because the compensation voltage value is calculated based on the subtraction value ΔVrq obtained by subtracting the droop value Dqs from the voltage deviation ΔVr. When the interconnection point current Is is inductive (that is, the delayed invalid current in the direction flowing out from the power converter 20 is negative), the voltage value V increases in proportion to the magnitude of the interconnection point current Is. When the interconnection point current Is is capacitive (that is, the delayed invalid current in the direction flowing out from the power converter 20 is positive), the voltage value V becomes smaller in proportion to the magnitude of the interconnection point current Is. Become.

Again, with reference to FIG. 9, the frequency control unit 220A includes a phase generation unit 221A and a droop calculator 228 (corresponding to "Fdp" in FIG. 9). When the AC system 101 is a single system, the compensation angular frequency Δω is not input to the adder 223. Therefore, the phase generation unit 221A subtracts the droop value obtained by multiplying the active power P by Dq from the reference angular frequency ω0, and generates the phase θ by time-integrating the subtracted value. Specifically, the phase generation unit 221A corresponds to a configuration in which the adder 223 in the phase generation unit 221 in FIG. 5 is replaced with an adder / subtractor 223A.

The droop calculator 228 receives the input of the active power P calculated by the active power calculation unit 205. The droop calculator 228 calculates the droop value Dps according to the active power P and outputs it to the adder / subtractor 223A. Specifically, the droop value Dps is a value obtained by multiplying the active power P by Dp, and is an angular frequency for correcting the angular frequency ω0. The coefficient Dp is a coefficient indicating the slope of the frequency droop characteristic in the droop calculator 228. It should be noted that the configuration may be such that an active current is used instead of the active power P.

FIG. 11 is a diagram showing frequency droop characteristics. The direction in which the active power P is output from the power converter 20 is the positive direction. Pmax is the maximum value of the active power P, and Pmin is the minimum value of the active power P. As shown in the frequency droop characteristic 611 of FIG. 11, the droop value Dps increases as the active power P increases.

Again, referring to FIG. 9, the adder / subtractor 223A time-integrators the angular frequency ω, which is the deviation between the reference angle frequency ω0 and the droop value Dps (that is, the value obtained by subtracting the droop value Dps from the reference angle frequency ω0). Output to 224. From this, the angular frequency ω becomes smaller as the active power P increases (that is, the droop value Dps increases). The time integrator 224 calculates the phase θ by time-integrating the angular frequency ω and outputs it to the command unit 250.

According to the configuration of the above modification, the frequency is adjusted according to the active power output by the power converter 20, and the voltage is adjusted according to the ineffective power. Therefore, the power converter 20 can be operated more stably. Further, for example, when power is transferred to an AC system 101 which is a single system by using a plurality of power converters 20, the output balance of each power converter 20 can be maintained.

Here, the frequency droop characteristic may be a non-linear characteristic as shown in FIG. FIG. 12 is a diagram showing a non-linear frequency droop characteristic. The direction in which the active power P is output from the power converter 20 is the positive direction.

With reference to FIG. 12, the non-linear frequency droop characteristic (hereinafter, also referred to as “non-linear droop characteristic”) includes the droop characteristic 621 when the active power P at the interconnection point is within the reference range and the active power P. It has a droop characteristic of 622,623 when it is out of the reference range. The slope of the droop characteristic 622,623 is larger than the slope of the droop characteristic 621.

In the example of FIG. 12, when the active power P is P2 ≦ P ≦ P1, the active power P is within the reference range. When Pmin ≦ P <P2 or P1 <P ≦ Pmax, the active power P is out of the reference range.

The droop calculator 228 calculates the droop value Dps according to the droop characteristic 621 when the active power P is within the reference range, and when the active power P is outside the reference range, the droop value Dps is calculated according to the droop characteristic 622,623. Is calculated. For example, if the active power P output from the power converter 20 increases more than expected for some reason, the active power P is out of the reference range. In this case, the droop value Dps increases sharply because it follows the droop characteristic 622. As a result, the angular frequency ω becomes sharply small, and the output from the power converter 20 falls within the expected range, so that the occurrence of overcurrent can be suppressed.

When the active power P output from the power converter 20 drops more than expected, the droop value Dps drops sharply and the angular frequency ω sharply increases. Even in this case, since the output from the power converter 20 is within the expected range, the occurrence of overcurrent can be suppressed.

<Shock mitigation when changing control method>
In FIG. 5, when it is determined that the AC system 101 has shifted to the single system, the control method of the frequency control unit 220 is changed by controlling the switch 225 to the OFF state. In this case, at the same time that the switch 225 is turned off, the compensation angular frequency Δω is not input to the adder 223.

Therefore, for example, when the compensation angular frequency Δω immediately before the single transition is large, the angular frequency ω may change abruptly to give a shock (for example, overcurrent) to the power converter 20. Therefore, a configuration will be described in which the compensation angular frequency Δω is gradually reduced when it is determined that the AC system 101 has shifted to the single system.

FIG. 13 is a diagram showing an example of the configuration of the frequency control unit for shock mitigation. With reference to FIG. 13, the frequency control unit 220X includes a phase generation unit 221X and an adjustment circuit 226. The phase generation unit 221X corresponds to a configuration in which the switch 225 in FIG. 5 is replaced with the switch 225X.

Here, when the AC system 101 is an interconnection system, the switch 225X is connected to the contact Ea side. When the independent system determination unit 211 determines that the AC system 101 has shifted to the independent system, it outputs a switching signal for switching the switch 225X from the contact Ea to the contact Eb to the switch 225X. As a result, the compensation angular frequency Δω is input to the adder 223 via the adjustment circuit 226.

The adjustment circuit 226 gradually reduces the compensation angular frequency ω0 after the AC system 101 shifts to the independent system. Specifically, the adjustment circuit 226 fixes the value at the compensation angle frequency Δω immediately before the AC system 101 shifts to the single system, and gradually reduces the fixed compensation angle frequency Δω. The adjustment circuit 226 is realized by, for example, a hold element and a washout filter that passes a change in the signal and cuts a stationary signal. For example, the adjustment circuit 226 changes the compensation angular frequency Δω as shown in FIG.

FIG. 14 is a diagram showing an example of a time change of the compensation angular frequency Δω. With reference to FIG. 14, the compensation angular frequency ωa is a value of the compensation angular frequency Δω output from the compensator 222 before switching the switch 225X from the contact Ea to the contact Eb side. The time ta is a time indicating the timing at which the switch 225X is switched to the contact Eb side by the switching signal from the independent system determination unit 211.

As shown in Graph 701, the compensation angular frequency Δω is maintained at the compensation angular frequency ωa during the period from time t to time ta. After the time ta has passed, it gradually decreases and finally becomes zero.

Again, referring to FIG. 13, the adder 223 outputs the added value of the compensation angular frequency Δω and the reference angular frequency ω0 reduced by the adjustment circuit 226 to the time integrator 224. The time integrator 224 generates the phase θ of the voltage command by time-integrating the added value.

According to the above configuration, even when the AC system 101 shifts to a single system, the compensation angular frequency Δω input to the adder 223 is gradually reduced, so that a sudden change in the angular frequency ω can be prevented. Can be done. As a result, the shock to the power converter 20 can be alleviated.

(Modification example)
FIG. 15 is a diagram showing another example of the configuration of the frequency control unit for shock mitigation. With reference to FIG. 15, the frequency control unit 220Y corresponds to a configuration in which a droop arithmetic unit 228 and an addition / subtraction unit 227 are added to the phase generation unit 221X of FIG. Here, as described with reference to FIG. 13, it is assumed that the AC system 101 has shifted to a single system and the switch 225X has been switched to the contact Eb.

The droop calculator 228X calculates the droop value Dps according to the active power P and changes the limiter in a ramp shape to output the droop value Dps to the addition / subtractor 227. As a result, the limiter changes linearly from 0, so that the droop value Dps more than expected is not output to the adder / subtractor 227.

The adder / subtractor 227 calculates the deviation between the compensation angular frequency Δω output from the adjustment circuit 226 and the droop value Dps, and outputs the deviation to the adder 223. In this case, the deviation changes as shown in FIG.

FIG. 16 is a diagram showing another example of the time change of the compensation angular frequency Δω. With reference to FIG. 16, the compensation angular frequency Δω changes as shown in Graph 703. Graphs 701 and 703 are the same in that the compensation angular frequency Δω is maintained at the compensation angular frequency ωa during the period from time t to time ta. However, after the time ta, the compensation angular frequency Δω according to the graph 703 changes more gradually than the compensation angular frequency Δω according to the graph 701. This is due to the influence of the droop value Dps.

Again, referring to FIG. 15, the adder 223 outputs the sum of the deviation between the compensation angular frequency Δω and the droop value Dps and the reference angular frequency ω0 to the time integrator 224. The time integrator 224 generates the phase θ of the voltage command by time-integrating the added value.

Even in this case, since the compensation angular frequency Δω input to the adder 223 is gradually reduced, it is possible to prevent a sudden change in the angular frequency ω and alleviate the shock to the power converter 20.

<Judgment method for transition to interconnection system (1)>
Here, a determination method for determining whether or not the generator 51 is connected to the AC system 101, which is a single system, and the AC system 101 has shifted to the interconnection system will be described.

FIG. 17 is a diagram showing an example of the functional configuration of the control device 10 for determining the transition of the AC system to the interconnection system. With reference to FIG. 17, the control device 10B has a configuration in which the overcurrent determination unit 270 and the interconnection system determination unit 272 are added to the control device 10 of FIG. 5, and the command unit 250 of FIG. 5 is replaced with the command unit 250B. Equivalent to. The control device 10B corresponds to the control device 10 shown in FIG. 1, but is provided with an additional reference numeral such as “B” for convenience in order to distinguish it from the control device 10 shown in FIG.

Here, a functional configuration different from the functions shown in FIG. 5 will be described. Further, it is assumed that the switch 225 is in the OFF state and the switch 260 is in the ON state. It is assumed that the control device 10B controls the power converter 20 by a control method (that is, a single system mode) when the AC system 101 is a single system.

The overcurrent determination unit 270 determines whether or not the interconnection point current Is is an overcurrent based on the absolute current value | Is | received from the current calculation unit 209. Specifically, the overcurrent determination unit 270 determines that the interconnection point current Is is an overcurrent if the absolute current value | Is | is equal to or greater than the threshold value Is |, and the absolute current value | Is | is less than the threshold value Is |. If, it is determined that the interconnection point current Is is not an overcurrent. The overcurrent determination unit 270 outputs the determination result to the command unit 250B.

The overcurrent determination unit 270 may perform overcurrent determination using each arm current Ipu, Inu, Ipv, Inv, Ipw, Inw instead of the interconnection point current. In this case, the overcurrent determination unit 270 determines that the arm current is overcurrent if at least one of the absolute values of each arm current is equal to or greater than the threshold value Iss, and all the absolute values of each arm current are less than the threshold value Iss. If so, it is determined that the arm current is not an overcurrent.

Upon receiving the determination result that the interconnection point current Is or the arm current is an overcurrent, the command unit 250B outputs a stop command for stopping the operation of the power converter 20 as a control command. Specifically, the stop command is a gate block command. As a result, the power converter 20 is in the gate block state, that is, the switching elements 22A and 22B of each submodule 7 are in the off state.

When the command unit 250B outputs a stop command to the power converter 20, it outputs GB information indicating that the power converter 20 is in the gate block state to the interconnection system determination unit 272.

The interconnection system determination unit 272 determines whether or not the AC system 101 has shifted from the single system to the interconnection system based on the GB information and the absolute voltage value | Vs |. Specifically, the interconnection system determination unit 272 receives GB information (that is, when the operation of the power converter 20 is stopped), and the absolute voltage value | Vs | is equal to or higher than the threshold value Vk. If, it is determined that the AC system 101 has shifted from the single system to the interconnection system. This is because, when the absolute voltage value | Vs | is equal to or higher than a certain value even though the operation of the power converter 20 is stopped, the power source other than the power converter 20 (that is, the generator 51) is an AC system. This is because it is considered to be connected to 101.

The interconnection system determination unit 272 outputs a determination result indicating that the AC system 101 has shifted to the interconnection system to the command unit 250B. Further, when it is determined that the interconnection system determination unit 272 has shifted to the interconnection system, the interconnection system determination unit 272 outputs an ON signal to the switch 225 and an OFF signal to the switch 260. As a result, the switch 225 is turned on and the switch 260 is turned off.

When the AC system 101 shifts to the interconnection system and the phase error Δθ becomes less than the threshold value θa, the command unit 250B issues a return command to the power converter 20 to restore the operation of the power converter 20. Output. Specifically, the return command is a deblock command. As a result, the power converter 20 is in a deblocked state, that is, a state in which the switching elements 22A and 22B of each submodule 7 can be turned on.

The operation flow of the control device 10B will be described with reference to FIG. FIG. 18 is a timing chart for explaining the operation of the control device 10B when the AC system shifts to the interconnection system. Here, for ease of explanation, the overcurrent determination unit 270 determines whether or not the interconnection point current Is is an overcurrent. With reference to FIG. 18, an overcurrent occurs at time t1. In this case, the overcurrent determination unit 270 determines that the absolute current value | Is | is equal to or greater than the threshold value Is |. Therefore, the command unit 250B outputs a gate block command to the power converter 20. As a result, the operation of the power converter 20 is stopped.

At time t2, when the absolute voltage value | Vs | becomes equal to or higher than the threshold value Vk when the power converter 20 is in the gate block state, the interconnection system determination unit 272 determines that the AC system 101 has shifted to the interconnection system. , The ON signal is output to the switch 225, and the OFF signal is output to the switch 260. As a result, the control method of the control device 10B is changed from the single system mode to the interconnection system mode. Immediately after the control method is changed, the phase difference between the phase θ of the voltage command and the phase of the interconnection point voltage Vs is large, so that the phase error Δθ increases sharply.

After that, the phase error Δθ gradually decreases due to the feedback control by the frequency control unit 220, and when the time t3 is reached, the phase error Δθ becomes less than the threshold value θa. This means that the phase θ of the voltage command is synchronized with the phase of the interconnection point voltage Vs. Therefore, at time t4, the command unit 250B outputs a deblock command to the power converter 20. As a result, the power converter 20 returns and continues operation according to the control method of the interconnection system mode.

With the above configuration, the control device 10B can accurately determine that the AC system 101 has shifted from the single system to the interconnected system. Further, when it is determined that the AC system 101 has shifted to the interconnection system, the operation of the power converter 20 is not immediately restored, but the phase error Δθ is reduced (that is, it is connected to the phase θ of the voltage command). When the synchronization with the phase of the system point voltage Vs is completed), the operation of the power converter 20 is restored. Therefore, it is possible to prevent the power converter 20 from being in an overcurrent state.

<Judgment method for transition to interconnection system (Part 2)>
Another determination method for determining whether or not the AC system 101 has shifted from the single system to the interconnection system will be described.

FIG. 19 is a diagram showing another example of the functional configuration of the control device 10 for determining the transition of the AC system to the interconnection system. With reference to FIG. 19, the control device 10C corresponds to a configuration in which the interconnection system determination unit 240 and the adder 241 are added to the control device 10A of FIG. The control device 10C corresponds to the control device 10 shown in FIG. 1, but is provided with an additional reference numeral such as “C” for convenience in order to distinguish it from the control device 10A of FIG.

Here, a functional configuration different from the functions shown in FIG. 9 will be described. Further, it is assumed that the switch 225 is in the OFF state and the switch 260 is in the ON state. It is assumed that the control device 10C controls the power converter 20 in the single system mode.

The interconnection system determination unit 240 adds the angular frequency fluctuation value Δω0 to the reference angle frequency ω0 of the power converter 20 to change the reference angle frequency ω0, so that the AC system 101 changes from a single system to an interconnection system. Judge whether or not it has moved to. The determination method of the interconnection system determination unit 240 will be specifically described with reference to FIGS. 20 to 23.

FIG. 20 is a model diagram for explaining a determination method of the interconnection system determination unit. Specifically, FIG. 20A is a model diagram when the AC system 101 is an interconnection system. FIG. 20B is a model diagram when the AC system 101 is a single system.

With reference to FIG. 20, the interconnection point 110 is an interconnection point to which the AC system 101 and the generator 51 or the load 45 are connected. In the case of FIG. 20A, since the generator 51 is connected to the interconnection point 110, the AC system 101 is an interconnection system. In the case of FIG. 20B, since the load 45 is connected to the interconnection point 110, the AC system 101 is a single system. The voltage at the interconnection point 110 is represented by V1.

The interconnection point 110 is an interconnection point between the AC system 101 and the power converter 20. The voltage at the interconnection point 110 is represented by V2. The active power and the ineffective power at the interconnection point 110 are represented by P and Q, respectively. The phase difference φ is the phase difference between the phase δ1 of the voltage V1 at the interconnection point 120 and the phase δ2 of the voltage V2 at the interconnection point 110. Further, the system impedance of the AC system 101 is represented by jx.

FIG. 21 is a diagram showing the relationship between the phase difference φ and the active power P. With reference to FIG. 21, the active power P changes in a parabolic shape with respect to the phase difference φ, and when the phase difference φ is 90 °, the active power P becomes the maximum value Pmax. This is the same regardless of whether the AC system 101 is a single system or an interconnected system. The fluctuation value ΔP of the active power P is determined according to the fluctuation value Δφ of the phase difference φ. The active power P is represented by the following equation (1).

P = {(V1 × V2) / x} sinφ ・ ・ ・ (1)
Therefore, the fluctuation value ΔP is expressed by the following equation (2).

ΔP = {(V1 × V2) / x} cosφ × Δφ ・ ・ ・ (2)
Since the generator 51 has inertia, the phase δ1 of the voltage at the interconnection point 110 does not change suddenly even if the reference angular frequency ω0 fluctuates. On the other hand, since the load 45 has no inertia, the phase δ1 of the voltage at the interconnection point 110 suddenly changes when the reference angular frequency ω0 fluctuates. Utilizing this fact, the interconnection system determination unit 240 determines whether or not the AC system 101 has shifted from the single system to the interconnection system.

FIG. 22 is a timing chart for explaining the determination method of the interconnection system determination unit 240. With reference to FIG. 22, the interconnection system determination unit 240 injects a positive fluctuation value Δω0 for a certain period of time Tx from the time tx1 to the time tx2 to change the reference angular frequency ω0 in the positive direction, and starts from the time tx2. During the period up to the time tx3, the fluctuation of the reference angular frequency ω0 is stopped without injecting the fluctuation value Δω0.

Subsequently, the interconnection system determination unit 240 injects a negative fluctuation value Δω0 for a certain period of time Tx from the time tx3 to the time tx4 to change the reference angular frequency ω0 in the negative direction. As a result, the reference angular frequency ω0 returns to the state before the fluctuation value Δω0 is injected, so that the occurrence of overcurrent and the occurrence of step-out can be suppressed.

When the AC system 101 is an interconnection system, the phase δ2 of the interconnection point 120 changes according to the equation δ = ∫ωdt when the reference angular frequency ω0 is changed. However, since the angular frequency ω and the phase δ1 of the interconnection point 110 cannot be suddenly changed due to the inertia of the generator 51 in the interconnection system, the fluctuation value Δφ of the phase difference φ changes in a mountain shape according to the change of the phase δ2. Therefore, the fluctuation value ΔP of the active power P also changes in a mountain shape.

On the other hand, when the AC system 101 is a single system, the phase δ1 of the interconnection point 110 can be suddenly changed by changing the reference angular frequency ω0 without being affected by the inertia of the generator 51. Further, when the load connected to the interconnection point 110 has a frequency characteristic, the load amount changes according to the change in the angular frequency, and the tide flow rate changes. As a result, the phase difference φ changes. That is, the fluctuation value Δφ of the phase difference φ changes following the fluctuation value Δω0. Therefore, the fluctuation value ΔP of the active power P also changes following the fluctuation value Δω0. The fluctuation value ΔP in the period from time tx1 to time tx2 is generally a multiplication value of the frequency characteristic constant of the load 45 and Δω0.

In the period in which the reference angular frequency ω0 is fluctuated in the positive direction and the fluctuation is temporarily stopped (that is, the period from time tx2 to time tx3), the value P1 of the fluctuation value ΔP when the AC system 101 is an interconnection system is Takes a non-zero value. The value P1 is generally a value obtained by substituting the fluctuation value Δω for the fluctuation value Δφ in the equation (2). On the other hand, in the period in which the fluctuation of the reference angular frequency ω0 is temporarily stopped, the value P2 of the fluctuation value ΔP when the AC system 101 is a single system becomes substantially zero.

Therefore, the interconnection system determination unit 240 shifts the AC system 101 to the interconnection system when the fluctuation value ΔP of the active power P is equal to or higher than the reference threshold Pth during the period in which the fluctuation of the reference angular frequency ω0 is temporarily stopped. Can be determined. Since the period from the start to the end of the fluctuation of the reference angular frequency ω0 (that is, the period of times tx1 to tx4) is within several hundred ms, the determination can be made in a short time.

FIG. 23 is a diagram showing an example of the configuration of the interconnection system determination unit 240. With reference to FIG. 23, the interconnection system determination unit 240 includes a frequency fluctuation unit 242, a fluctuation value calculation unit 243, and a determination unit 245. Here, it is assumed that the switch 225 is in the OFF state and the power converter 20 is controlled in the single system mode.

The frequency fluctuation unit 242 fluctuates the reference angular frequency ω of the power converter 20 when the active power P at the interconnection point between the AC system 101 and the power converter 20 is out of the reference range. Specifically, the frequency fluctuation unit 242 inputs the fluctuation value Δω0 to the adder 241 when the active power P is out of the reference range.

Typically, the frequency fluctuation unit 242 inputs the fluctuation value Δω0 to the adder 241 as described with reference to FIG. 22. After the frequency fluctuation unit 242 changes the reference angular frequency ω0 by Tx in the first polar direction (for example, the positive direction) for a certain period of time, the fluctuation of the reference angular frequency ω0 is stopped. Further, the frequency fluctuation unit 242 stops the fluctuation of the reference angular frequency ω0 in the first polar direction, and then keeps the reference angular frequency ω0 constant in the second polar direction (for example, the negative direction) opposite to the first polar direction. Fluctuate time Tx. The adder 241 outputs the sum of the reference angular frequency ω0 and the fluctuation value Δω0 to the adder / subtractor 223A. As a result, the frequency of the voltage output from the power converter 20 fluctuates.

The fluctuation value calculation unit 243 changes the reference angle frequency ω0 by Tx in the first polar direction for a certain period of time, and then stops the fluctuation of the reference angle frequency ω0. The fluctuation value ΔP of is calculated. Specifically, the fluctuation value calculation unit 243 calculates the fluctuation value ΔP of the active power P in the period of time tx2 to time tx3 in FIG. 22.

The determination unit 245 determines whether or not the AC system 101 has shifted from the single system to the interconnection system based on the fluctuation value ΔP of the active power P at the time when the fluctuation of the reference angular frequency ω0 is stopped. Specifically, the determination unit 245 determines that the AC system 101 has shifted from the single system to the interconnection system when the fluctuation value ΔP is equal to or higher than the reference threshold value Pth, and when the fluctuation value ΔP is less than the reference threshold value Pth. It is determined that the AC system 101 has not been transferred to the interconnection system (that is, the AC system 101 is a single system).

When the determination unit 245 determines that the AC system 101 has shifted to the interconnection system, the determination unit 245 outputs an ON signal to the switch 225 and an OFF signal to the switch 260. As a result, the switch 225 is turned on and the switch 260 is turned off, so that the power converter 20 operates according to the control method in the interconnection system mode.

The control device 10C may be configured to determine the transition of the AC system 101 to the interconnection system while executing frequency control according to the frequency droop characteristic shown in FIG. In this case, the control device 10C determines the transition of the AC system 101 to the interconnection system while adjusting the frequency according to the active power output by the power converter 20.

Further, the control device 10C may be configured to determine the transition of the AC system 101 to the interconnection system while executing the frequency control according to the non-linear frequency droop characteristic shown in FIG. When the AC system 101 has been transferred from the single system to the interconnection system, the active power P output from the power converter 20 increases more than expected, and the active power P is out of the reference range. In this case, the droop value Dps follows the droop characteristic 622 and therefore increases sharply, and the angular frequency ω sharply decreases. This enables frequency control following the AC system 101.

Therefore, the output from the power converter 20 is within the expected range, and the occurrence of overcurrent can be suppressed. Therefore, the control device 10C can determine whether or not the AC system 101 has shifted from the single system to the interconnected system while continuing the operation by suppressing the generation of overcurrent.

In this case, the control device 10C changes the reference angular frequency ω when the active power P is out of the reference range (that is, Pmin ≦ P <P2 or P1 <P ≦ Pmax). This is because when the active power P satisfies Pmin ≦ P <P2 or P1 <P ≦ Pmax, there is a high possibility that the AC system 101 has shifted to the interconnection system.

According to the above configuration, the control device 10C can accurately determine that the AC system 101 has shifted from the single system to the interconnected system. Further, by returning the reference angular frequency ω0 to the state before injecting the fluctuation value Δω0, it is possible to suppress the occurrence of overcurrent and the occurrence of step-out. Further, since the period from the start to the end of the fluctuation of the reference angular frequency ω0 is within several hundred ms, the transition determination can be performed in a short time.

Other embodiments.
(1) In the above-described embodiment, as shown in FIG. 1, the configuration in which the power converter 21 is connected to the power converter 20 via the DC transmission line 14 has been described, but the configuration is limited to this configuration. Absent. Specifically, instead of the generator 63, the transformer 61, the AC system 102, and the power converter 21, a DC power source capable of supplying DC power may be connected to the power converter 20.

FIG. 24 is a diagram showing another example of the configuration of the power control system. With reference to FIG. 24, a DC power supply 65 is connected to the power converter 20. The DC power source 65 is, for example, a storage battery, a solar power generation device, a fuel cell, or the like.

(2) The voltage control unit in the above-described embodiment is not limited to the above configuration, and may have, for example, the configuration shown in FIG. 25. FIG. 25 is a diagram showing a modified example of the configuration of the voltage control unit. With reference to FIG. 25, the voltage control unit 230X corresponds to a configuration in which a droop arithmetic unit 237, 238 and an adder 239 are added to the voltage control unit 230 of FIG. Further, the control device 10 further includes an adder / subtractor 264.

The adder / subtractor 264 calculates the ineffective power deviation ΔQr between the reference ineffective power Qref and the ineffective power Q calculated by the ineffective power calculation unit 207. The invalid power deviation ΔQr output from the adder / subtractor 264 is input to the droop calculator 237 of the voltage control unit 230X.

The droop calculator 237 calculates a droop value according to the invalid power deviation ΔQr and outputs it to the adder / subtractor 239. Specifically, the droop calculator 237 calculates the droop value Dqr by multiplying the invalid power deviation ΔQr by Kq, and outputs it to the adder / subtractor 239. The coefficient Kq is a coefficient indicating the slope of the droop characteristic of the droop calculator 237. The droop calculator 237 corresponds to the droop calculator 235 shown in FIG.

The droop calculator 238 calculates the droop value according to the voltage deviation ΔVr and outputs it to the adder / subtractor 239. Specifically, the droop calculator 238 calculates the droop value Dvr by multiplying the voltage deviation ΔVr by Kv, and outputs it to the adder / subtractor 239. The coefficient Kv is a coefficient indicating the slope of the droop characteristic of the droop calculator 238.

The adder 239 outputs the added value Vqv of the droop value Dqr and the droop value Dvr to the compensator 231. The compensator 231 calculates the compensation voltage value by performing a primary delay process on the value compensated for the added value Vqv, and outputs the compensation voltage value to the addition / subtractor 232. Specifically, the PI controller 231x outputs a value feedback-controlled so as to compensate the added value Vqv to the first-order lag element 231y. The first-order lag element 231y performs filtering processing by the transfer function G1 on the output value from the PI controller 231x to calculate the compensation voltage value, and outputs the compensation voltage value to the addition / subtractor 232. The configuration of the adder / subtractor 232 and the configuration of the droop arithmetic unit 234 are the same as those described with reference to FIG. 7.

In the above configuration, for example, when Kv = 1 and Kq = 0 are set, the control device 10 operates the power converter 20 by a constant voltage control method that controls the output voltage of the power converter 20 to be constant. Further, when Kv = 0 and Kq = 1, the control device 10 operates the power converter 20 by the ineffective power constant control method that constantly controls the ineffective power output of the power converter 20.

When Kv = 1 and 0 <Kq <1 are set, the control device 10 operates the power converter 20 while adjusting the output voltage according to the invalid power output of the power converter 20. When 0 <Kv <1 and Kq = 1 are set, the control device 10 operates the power converter 20 while adjusting the invalid power output according to the output voltage of the power converter 20. The coefficients Kq and Kv may be appropriately changed by the system operator or may be appropriately changed according to the system voltage of the power system.

(3) In the above-described embodiment, the configuration in which the power converters 20 and 21 are modular multi-level converters has been described, but the configuration is not limited to this. For example, the circuit system of the power converters 20 and 21 may be composed of a two-level converter that converts AC power into two-level DC power, or a three-level converter that converts AC power into three-level DC power. It may be composed of a converter.

(4) The configuration exemplified as the above-described embodiment is an example of the configuration of the present invention, can be combined with another known technique, and a part thereof is not deviated from the gist of the present invention. It is also possible to change the configuration by omitting it. Further, in the above-described embodiment, the process or configuration described in the other embodiments may be appropriately adopted and carried out.

It should be considered that the embodiments disclosed this time are exemplary in all respects and not restrictive. The scope of the present invention is shown by the scope of claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims.

4u, 4v, 4w leg circuit, 5 upper arm, 6 lower arm, 7 submodule, 8A, 8B reactor, 9A, 9B arm current detector, 10,10A, 10B, 10C, 12 controller, 11A, 11B DC voltage Detector, 13,61 transformer, 14,14N, 14P DC transmission line, 20,21 power converter, 22A, 22B switching element, 23A, 23B diode, 24 DC capacitor, 25 conversion circuit, 27 DC voltage detector, 28 Transmitter / receiver, 29 Gate control, 32,33 Bus, 34,35,36 Breaker, 41,42,45 Load, 51,63 Generator, 55 Auxiliary transformer, 56 Signal converter, 65 DC power supply, 70 Arithmetic processing unit, 71 bus, 72 CPU, 73 ROM, 74 RAM, 75 DI circuit, 76 DO circuit, 77 input interface, 78 communication interface, 81 AC voltage detector, 82 AC current detector, 101, 102 AC system, 110, 120 interconnection points, 201 voltage calculation unit, 202 dq conversion unit, 203 voltage calculation unit, 204 phase error calculation unit, 205 active power calculation unit, 207 invalid power calculation unit, 209 current calculation unit, 211 single system determination unit , 220, 220A, 220X, 220Y frequency control unit, 221,221A, 221X phase generator, 222,231 compensator, 224 integrator, 225,225X, 260 switch, 226 adjustment circuit, 228,228X, 234,235, 237,238 Droop calculator, 230, 230A, 230X Voltage control unit, 231x PI controller, 231y primary delay element, 234x incomplete differential element, 234y droop coefficient element, 240, 272 interconnection system determination unit, 242 frequency fluctuation unit 243 Fluctuation value calculation unit, 245 judgment unit, 250, 250B command unit, 270 overcurrent judgment unit, 301 voltage judgment circuit, 302, 303 phase judgment circuit, 304 change rate judgment circuit, 305 OR circuit, 306 AND circuit.

Claims (11)

A control device for controlling a self-excited power converter connected to an AC system.
A phase generator that generates the phase of the voltage command of the power converter,
A voltage control unit that generates the voltage value of the voltage command and
A command unit for outputting the voltage command having the generated phase and the voltage value to the power converter is provided.
The voltage control unit
A voltage compensation unit that calculates a compensation voltage value based on the voltage deviation between the reference voltage and the interconnection point voltage at the interconnection point between the AC system and the power converter.
When the AC system is a single system that is not connected to a generator, a droop calculation unit that calculates a first droop value according to the magnitude of the interconnection point current flowing through the interconnection point, and a droop calculation unit.
A control device including a calculation unit that calculates a voltage value of the voltage command based on a deviation between the compensation voltage value and the first droop value. The voltage compensation unit calculates the compensation voltage value by performing a primary delay process on the value compensated for the voltage deviation.
The control device according to claim 1, wherein the droop calculation unit calculates the first droop value by incompletely differentiating the absolute value of the interconnection point current and multiplying it by a first coefficient. The control device according to claim 1 or 2, wherein the calculation unit calculates a deviation between the compensation voltage value and the first droop value as a voltage value of the voltage command. The voltage compensating unit subtracts a second droop value obtained by multiplying the reactive power at the interconnection point by a second coefficient from the voltage deviation, and calculates the compensating voltage value based on the subtracted value. 1 or the control device according to claim 2. The aspect according to any one of claims 1 to 4, wherein when the AC system is the single system, the phase generator generates the phase of the voltage command by time-integrating the reference angular frequency. Control device. When the AC system is the single system, the phase generator subtracts a third droop value obtained by multiplying the active power at the interconnection point by a third coefficient from the reference angular frequency, and the subtracted value is the time. The control device according to any one of claims 1 to 4, wherein the phase of the voltage command is generated by integrating. The third coefficient is a coefficient indicating the slope of the frequency droop characteristic.
The frequency droop characteristic is non-linear having a first droop characteristic when the active power at the interconnection point is within the reference range and a second droop characteristic when the active power at the interconnection point is outside the reference range. It is a droop characteristic,
The control device according to claim 6, wherein the inclination of the second droop characteristic is larger than the inclination of the first droop characteristic. Further, a phase error calculation unit for calculating the phase error between the phase of the voltage command of the power converter and the phase of the interconnection point voltage is provided.
The phase generator
Calculate the compensation angular frequency to compensate for the phase error,
After the AC system is transferred to the single system, the compensation angular frequency is gradually reduced.
The control device according to any one of claims 1 to 4, wherein the phase of the voltage command is generated by time-integrating the added value of the compensation angular frequency and the reference angular frequency of the power converter. Further, a phase error calculation unit for calculating the phase error between the phase of the voltage command of the power converter and the phase of the interconnection point voltage is provided.
The phase generator
Calculate the compensation angular frequency to compensate for the phase error,
After the AC system is transferred to the single system, the compensation angular frequency is gradually reduced.
The deviation between the compensation angular frequency and the third droop value obtained by multiplying the active power at the interconnection point by a third coefficient is calculated.
The control device according to any one of claims 1 to 4, wherein the phase of the voltage command is generated by time-integrating the added value of the deviation and the reference angular frequency of the power converter. The control device according to any one of claims 1 to 9, wherein the power converter is a power converter that performs power conversion between the AC system and the DC system. The power converter includes a first arm and a second arm.
Each of the first arm and the second arm includes a plurality of submodules connected in series with each other.
The control device according to any one of claims 1 to 10, wherein each submodule includes a switching element and a diode and a capacitor connected in parallel to the switching element.

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